Within the television (TV) industry, aspect ratio is defined to be the ratio of the width of a picture to its height. In the present United States television picture as specified by the National Television Standards Committee (NTSC), the aspect ratio is 4 to 3. A motion picture screen in a commercial theater has an aspect ratio of at least 5 to 3. Studies have shown that the present NTSC television picture aspect ratio of 4 to 3 is not desirable from a human factors point of view for certain types of production techniques. For example, the article entitled "High-Definition Wide-Screen Television System for the Future", Takashi Fujio, IEEE Transactions On Broadcasting, Vol. BC-26, No. 4, Dec. 1980, pp. 113-124, indicates that the 5 to 3 aspect ratio is desirable for a television picture. The desirability of a larger aspect ratio than the present NTSC becomes much more important when the resolution of the picture is increased. The higher resolution picture allows scenes to be displayed at a distance rather than only close up while still retaining picture detail. Since many production techniques can make advantageous use of a wider screen for displaying scenes at a distance, the need for a larger aspect ratio arises. However, it has long been recognized that the human eye tends to focus on the center of a screen and is not conscious of the edges. Hence, the same degree of resolution is not needed at the edge of a picture as required at the center.
An approach to providing high-definition television that could be received as a conventional television picture by conventional television receivers operating according to the NTSC standard or that could be received as a high-definition television picture by newly designed receivers without requiring prohibitively large amounts of bandwidth is disclosed in the above-identified application of T. S. Rzeszewski 1, "Fully Compatible High-Definition Television", Ser. No. 462,065. In that system, one television channel carries the conventional information while high-frequency luminance and high-frequency chrominance information are provided in a second television channel. That system has an aspect ratio of 4 to 3. Whereas, for many applications the aspect ratio of 4 to 3 is suitable, there exist applications for which a greater aspect ratio is desirable.
Therefore, there exists a need for a high-definition television system that is compatible with the standard NTSC system but that can also provide improved aspect ratio information without requiring a greater bandwidth than that provided by two television channels.